Two-cycle

Vegetable and seed oils as well as some synthetic base stocks present a new class of biodegradable base stocks. These fluids (10) have excellent biodegradation properties as measured by criteria developed by the Environmental Protection Agency (EPA) or Organization of Economic Cooperation and Development (OECD). OECD 301 and EPA 560/6-82-003 measure the biodegradation of lubricants. These tests were developed to measure the degradation of oil, especially two-cycle ok, on waterways. Aquatic toxicity criteria toward fish is also found to be acceptable for this class of fluids as measured by EPA 560/6-82-002 and OECD 203 1-12. 

Oil viscosity grades have also been developed with suitable additives for use in a variety of specific appHcations in two-cycle engines, refrigeration and air conditioning, oil mist lubricators, low outdoor temperatures, instmments, and office machines as partially reflected in Table 3. Equipment manufacturers and lubricant suppHers provide recommendations for individual cases. 

Esters generally tend to be readily biodegradable. This is advantageous for two-cycle engine oils which are discharged to the surroundings from power-driven recreational boats and various portable power units around the home. 

PoUowing further development (38), a two-cycle process has been adopted by industry. In the first concentration cycle, the clarified feed acid containing 100—200 mg/L U Og [1334-59-8] is oxidized, for example, with hydrogen peroxide or sodium chlorate [7775-09-9] to ensure that uranium is in its 6+ valence state is not extracted. Uranium is extracted with a solvent composed of 0.5 Af D2EHPA and 0.125 Af TOPO dissolved in an aUphatic hydrocarbon diluent. 

Branched-chain acids have a wide variety of industrial uses as paint driers (7), vinyl stabilizers (8), and cosmetic products (9). Cobalt and manganese salts of 2-ethyIhexanoic acid and neodecanoic acid are used as driers for paint, varnishes, and enamels litbium, magnesium, calcium, and aluminum salts of 2-ethyIhexanoic acid are used in the formation of greases and lubricants (see Driers and metallic soaps). Derivatives of isostearic acid have been used as pour point depressants in two-cycle engine oils, as textile lubricants, and in cosmetic formulations. Further industrial appHcations can be found (10). 

Short-circuit protection. To provide an instantaneous tripping on a short-circuit delay of, say, one or two cycles may be introduced into the tripping circuit to bypass any transient currents and avoid an unwanted trip. 

The exergy equation (2.26) enables useful information on the irreversibilities and lost work to be obtained, in comparison with a Carnot cycle operating within the same temperature limits (T ,ax = Ey and T in = To). Note first that if the heat supplied is the same to each of the two cycles (Carnot and IJB), then the work output from the Carnot engine (Wcar) is greater than that of the IJB cycle (Wijg), and the heat rejected from the former is less than that rejected by the latter. 

Fig. 4.2. Temperalure-en(ropy diagram for single-step cooling—equivalent two cycles (after Ref. [5 ).

Analytically, the efficiency of this combination of the two cycles may be expressed as... 

Here, we first discuss whether such semi-closure (which is introduced so that CO2 separation can be undertaken more easily) is likely to lead to higher or lower thermal efficiency, and in this discussion it is helpful to consider recirculation in relation to an air standard cycle (see Fig. 8.4). Fig. 8.4a shows a closed air standard cycle with unit air flow Fig. 8.4b shows an open cycle similarly with unit air flow and an air heater rather than a combustion chamber. The cycles are identical in every respect except that in the former the turbine exhaust air from the turbine is cooled before it re-enters the compressor. In the latter, the turbine exhaust air is discharged to atmosphere and a fresh charge of air is taken in by the compressor. The quantities of heat supplied and the work output are the same for each of the two cycles, so that the thermal efficiencies are identical. 

We can then add the two cycles together as shown in Fig. 8.4c, to form a semi-closed plant. There is double the flow through this new plant, double the heat supply and double the work output. Strictly, the total heat rejected is not doubled half the turbine exhaust is now discharged to the atmosphere and half the heat rejected into a cooler before it is recirculated into the compressor. The thermal efficiency of this double semi-closed plant is unchanged from that of the original closed cycle and the original open cycle. So there is apparently no thermodynamic advantage in semi-closure it is undertaken for a different purpose. 

Figure 16-3. In lliis cross section of a two-cycle engine, only a trained eye can identify the engine porting that distinguishes it from a four-cycle engine. (Courtesy of Electro-Motive Division, General Motors Corp., and Stewart and Stevenson Services, Inc.)...

The enzymes of the glyoxylate cycle in plants are contained in glyoxysomes, organelles devoted to this cycle. Yeast and algae carry out the glyoxylate cycle in the cytoplasm. The enzymes common to both the TCA and glyoxylate pathways exist as isozymes, with spatially and functionally distinct enzymes operating independently in the two cycles. 

Harmonics or multiples of 2, 3, 4, etc., of this frequency will exist and be dominant for two-cycle gas engines, and one half multiples will be dominant for four-cycle engines. If several single-acting cylinders are operating on the same system in parallel, the magnitude of the pulses will depend upon the combination of cylinders and crank throws, and this magnitude is additive for the simultaneous waves in phase. 

The four-cycle engine takes two complete piston strokes for exhaust, scavenging, and charging. The two-cycle engine exhausts, scavenges, and charges for about 25% of its piston travel before bottom center, and until about 25% after bottom center. The two-cycle machine does not have intake and exhaust valves but uses ports. 

N = number of power strokes per minute. For two cycle engines, N = engine rpm, for four-cycle engine,... 

There can also be a combination of the two cycles in an engine. Such an engine is called a mixed, combination, or limited pressure cycle. 

With the downhole power available and the signal detection threshold at surface, Figure 4-254b gives the maximum depth that can be reached by the technique as a function of frequency. Assuming that phase-shift keying is used with two cycles per bit, in a 10 fi m area (such as the Rocky mountains) a depth of 2 km (6,000 ft) could be reached while transmitting 7 bits/s. 

However, the intervals or frequencies generated by these machines are not always associated with one complete revolution of a shaft. In a two-cycle reciprocating engine, the pistons complete one cycle each time the crankshaft completes one 360° revolution. In a four-cycle engine, the crank must complete two complete revolutions, or 720°, in order to complete a cycle of all pistons. 

In a two-cycle machine, all pistons complete a full cycle each time the crankshaft completes one revolution. Figure 44.9 illustrates the normal action of a two-cycle, or single-action, compressor. Inlet and discharge valves are located in the clearance space and connected through ports in the cylinder head to the inlet and discharge connections. 

Figure 44.9 Two-cycle, or single-action, air compressor cylinders...

Crankshaft drives of rigidly mounted large two-cycle engines. 

Certain measures re.spond particularly strongly to the intrinsic structural symmetry of r lattices cycle number (= C ) enumeration, for example, does not identify two cycles all of whose states are related by a spatial translation. Specific profiles may, therefore, be interrupted by a series of pronounced peaks at gj = (see figures (3.47-a,d), (3.48-d) and (3.49-a), for example). 

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